Crt Having a Low Moire Transformation Function

Abstract

The CRT (10) according to the invention has an envelop (11) including a panel (12) attached to a funnel (15), the funnel having a neck (14) and an electron gun (26) for generating at least one electron beam (28) contained in the neck. A mask (25) is contained in the envelop near the panel. A region of the mask has columns (30) of apertures (31) of predetermined heights and predetermined pitches. The at least one electron beam has a spot size range and spot shape selected such that the moiré transformation function for the CRT in the region is less than about 0.02, wherein the moiré transformation function is a quotient having a numerator being the difference between a maximum value and a minimum value of mask transmission and a denominator being the sum of the maximum and the minimum values. The mask transmission is the percentage of electrons of a spatially uniform electron beam incident on the mask that can propagate therethrough the apertures averaged over a plurality of adjacent mask aperture columns and the regions containing the maximum and minimum values are adjacent to each other.

Description

FIELD OF THE INVENTION[0001]The invention relates to a color cathode-ray tube (CRT) and, more particularly to a color CRT having a reduced propensity for visible moiré over a plurality scan line modes.BACKGROUND OF THE INVENTION[0002]The current trend in the television industry is to provide displays to consumers which have clear crisp images with high resolution. As such, the television industry is challenged to broadcast and transmit signals which are digital and have high definition. Further, the industry is challenged to manufacture display devices, including those with the cathode ray tube (CRT), which can receive and display high definition digital signals and display such corresponding images in high resolution.[0003]Regarding CRTs, to provide the end user with higher resolution images (i.e. images having increasingly more and smaller screen structure elements), CRT designers and manufacturers are also challenged to produce CRTs with electron beam spot sizes that are increasi...

AI Technical Summary

Benefits of technology

The invention is a cathode ray tube (CRT) with a panel and funnel. The panel has a luminescent screen with phosphor stripes and a mask with columns of apertures. The electron beam emitted by the electron gun in the funnel scans across the mask and impinges on the phosphor stripes. The electron beam has a spot size that changes as it scans, which reduces the perceptible moiré effect. The CRT has a moiré transformation function of less than 0.0, which can be controlled by adjusting the electron beam spot size, mask aperture pitch, and tie bar height. The technical effects of the invention are improved image quality and reduced moiré effect.

Problems solved by technology

As such, the television industry is challenged to broadcast and transmit signals which are digital and have high definition.

Further, the industry is challenged to manufacture display devices, including those with the cathode ray tube (CRT), which can receive and display high definition digital signals and display such corresponding images in high resolution.

It is well understood by those in the CRT industry that as the resolution increases, the manufacture of CRTs become inherently more difficult.

The CRT designers and manufactures are even further challenged by the fact that as the television industry progresses toward higher resolution displays and HDTV (high definition television), the number of scan mode types (correlating to the number of scan lines) have proliferated. FIG. 1 shows a plot of some various scan modes that have been used or considered.

The difficulty is that the modern day and future CRT designs may be expected to accommodate certain desired resolutions at many different scan modes.

However, CRTs (as shown in FIG. 2), when used to accommodate a variety of scan line modes, unfortunately may exhibit undesirable moiré at some of these scan modes.

This may appear to be an ideal condition where no moiré would be observed (because theoretically the moiré pitch approaches infinity); however, this is actually not desired because when a CRT is designed to operate in such a manor, it is extremely difficult, if not impossible, to have the electron beam profiles (or scan line positions) not deviate from the mask transmission profile.

Unfortunately, in practice when a CRT is designed to operate as that in FIG. 5, the deviation of electron beam profiles (or scan line positions) with respect to the mask transmission profile becomes visible to a viewer.

What has also been problematic in CRTs having increased resolution is the effect of self-convergence that takes place when the electron beams are deflected by the horizontal deflection field of self-converging systems.

The amount of dynamic focus correction can be decreased to reduce or eliminate this moiré, but this increases the spot size and reduces the resolution.

Images